/*
 * Copyright 2000-2015 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.util;

import com.intellij.util.containers.SingletonIterator;
import gnu.trove.TObjectHashingStrategy;
import org.jetbrains.annotations.NotNull;

import java.lang.reflect.Array;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;

/**
 * Read-only set consisting of the only element
 */
public class SingletonSet<E> implements Set<E> {
    private final E theElement;

    public SingletonSet(E e) {
        theElement = e;
    }

    @Override
    public int size() {
        return 1;
    }

    @Override
    public boolean contains(Object elem) {
        //noinspection unchecked
        return getStrategy().equals(theElement, (E) elem);
    }

    @NotNull
    @Override
    public Iterator<E> iterator() {
        return new SingletonIterator<E>(theElement);
    }

    @NotNull
    @Override
    public Object[] toArray() {
        return new Object[]{theElement};
    }

    @NotNull
    @Override
    public <T> T[] toArray(@NotNull T[] a) {
        if (a.length == 0) {
            //noinspection unchecked
            a = (T[]) Array.newInstance(a.getClass().getComponentType(), 1);
        }
        //noinspection unchecked
        a[0] = (T) theElement;
        if (a.length > 1) {
            a[1] = null;
        }
        return a;
    }

    @Override
    public boolean add(E t) {
        throw new IncorrectOperationException();
    }

    @Override
    public boolean remove(Object o) {
        throw new IncorrectOperationException();
    }

    @Override
    public boolean containsAll(@NotNull Collection<?> c) {
        for (Object e : c) {
            if (!contains(e)) {
                return false;
            }
        }
        return true;
    }

    @Override
    public boolean addAll(@NotNull Collection<? extends E> c) {
        throw new IncorrectOperationException();
    }

    @Override
    public boolean retainAll(@NotNull Collection<?> c) {
        throw new IncorrectOperationException();
    }

    @Override
    public boolean removeAll(@NotNull Collection<?> c) {
        throw new IncorrectOperationException();
    }

    @Override
    public void clear() {
        throw new IncorrectOperationException();
    }

    @Override
    public boolean isEmpty() {
        return false;
    }

    @NotNull
    protected TObjectHashingStrategy<E> getStrategy() {
        //noinspection unchecked
        return TObjectHashingStrategy.CANONICAL;
    }

    @NotNull
    public static <T> Set<T> withCustomStrategy(T o, @NotNull TObjectHashingStrategy<T> strategy) {
        return new CustomStrategySingletonSet<T>(o, strategy);
    }

    private static class CustomStrategySingletonSet<E> extends SingletonSet<E> {
        @NotNull
        private final TObjectHashingStrategy<E> strategy;

        private CustomStrategySingletonSet(E e, @NotNull final TObjectHashingStrategy<E> strategy) {
            super(e);
            this.strategy = strategy;
        }


        @Override
        @NotNull
        protected TObjectHashingStrategy<E> getStrategy() {
            return strategy;
        }
    }
}
